The present invention relates to an optical pick-up device which at least either records information on an optical information recording medium on which information is recorded through the use of holography, or reproduces information from the optical information recording medium.
Holographic recording for recording information on a recording medium through the use of holography is typically performed by superimposing light that carries image information on reference light within the recording medium and by writing the resulting interference pattern onto the recording medium. For reproducing the information recorded, the recording medium is irradiated with reference light so that the image information is reproduced through diffraction derived from the interference pattern.
Recently, volume holography, or digital volume holography in particular, has been developed and is attracting attention in practical fields for ultra-high density optical recording. Volume holography is a method for writing a three-dimensional interference pattern by making positive use of a recording medium in the direction of thickness as well, and is characterized in that it is possible to enhance the diffraction efficiency by increasing the thickness and to achieve a greater recording capacity by employing multiplex recording. Digital volume holography is a computer-oriented holographic recording method which uses the same recording medium and recording method as with the volume holography, whereas the image information to be recorded is limited to binary digital patterns. In the digital volume holography, analog image information such as a picture is once digitized and developed into two-dimensional digital pattern information, and then it is recorded as image information. For reproduction, this digital pattern information is read and decoded to restore the original image information for display. Consequently, even if the SN ratio (signal-to-noise ratio) in the reproduction is somewhat poor, it is possible to reproduce the original information with extremely high fidelity by performing differential detection and/or error correction on encoded binary data.
In conventional holographic recording, a recording medium itself contains no information intended for positioning. Therefore, positioning of information light and reference light with respect to the recording medium is possible only mechanically, which makes a precise positioning difficult. On that account, the conventional holographic recording has such disadvantages that random access to the recording medium is difficult and high density recording is also difficult.
Under the circumstances, it is conceivable that the recording medium intended for holographic recording may be formed into a plate-like ordinary optical disks such as a CD (compact disk), and a recording/reproducing apparatus intended for holographic recording may be configured so that an optical pick-up device including an optical system for recording information on and reproducing information from the recording medium is rendered movable with respect to the recording medium.
In ordinary optical disk devices, focus servo and tracking servo are performed typically by driving an objective lens in the optical pick-up device. Under such configuration, vibrations externally applied to the optical pick-up device cause relative vibrations between the objective lens and the other parts in the optical system. Those vibrations, even if they are of a magnitude as low as to be insignificant to ordinary optical disk devices, affect the recording and reproduction operations greatly in the case of holographic recording. More specifically, in the case of holographic recording, even the slightest vibrations of the optical system under recording can cause a large change in the interference pattern to thereby preclude accurate recording of information. Under reproduction, a shift in positional relationship between the reference light for reproduction and the interference pattern may hamper accurate reproduction of information.
Similarly, in holographic recording, a relative inclination between the recording medium and the optical pick-up device has a greater impact than in ordinary optical disk devices.
Thus, in holographic recording, the use of an optical pick-up device having the same structure as that of an ordinary optical disk device results in the problem that vibrations externally applied to the optical pick-up device and fluctuations in the relative positional relationship between the optical pick-up device and the recording medium deteriorate recording and reproduction accuracies to a greater extent than in the case of ordinary optical disk devices.
An object of the invention is to provide an optical pick-up device for at least either recording information on an optical information recording medium on which information is recorded through the use of holography, or reproducing information from the optical information recording medium, which make it possible to prevent deterioration of recording and reproduction accuracy resulting from external vibrations or fluctuations in the relative positional relationship with the recording medium.
An optical pick-up device of the invention comprises:
a pick-up body for at least either recording information on an optical information recording medium on which information is recorded through the use of holography, or reproducing information from the optical information recording medium; and
position adjusting means for adjusting a position of the pick-up body in order to correct a shift in a relative positional relationship between the pick-up body and the optical information recording medium.
In the optical pick-up device of the invention, the position adjusting means adjusts the position of the pick-up body, whereby a shift in the relative positional relationship between the pick-up body and the optical information recording medium is corrected.
In the optical pick-up device of the invention, the position adjusting means may change the position of the pick-up body in a direction perpendicular to a surface of the optical information recording medium, in a direction parallel to the surface of the optical information recording medium, and in such a direction as to change an inclination of the pick-up body with respect to the surface of the optical information recording medium.
In the optical pick-up device of the invention, the pick-up body may comprise: information light generation means for generating information light carrying information; recording-specific reference light generation means for generating recording-specific reference light; and a recording optical system for irradiating the optical information recording medium with the information light and the recording-specific reference light from the same side so that information is recorded on the optical information recording medium in the form of an interference pattern resulting from interference between the information light and the recording-specific reference light. In this case, the recording optical system may perform the irradiation with the information light and the recording-specific reference light so that an optical axis of the information light and an optical axis of the recording-specific reference light are located on the same line.
In the optical pick-up device of the invention, the pick-up body may comprise: reproduction-specific reference light generation means for generating reproduction-specific reference light; a reproducing optical system for irradiating the optical information recording medium with the reproduction-specific reference light and collecting reproduction light generated from the optical information recording medium on the same side as that from which the optical information recording medium is irradiated with the reproduction-specific reference light; and detection means for detecting the reproduction light collected by the reproducing optical system. In this case, the reproducing optical system may perform the irradiation with the reproduction-specific reference light and the collection of the reproduction light so that an optical axis of the reproduction-specific reference light and an optical axis of the reproduction light are located on the same line.
In the optical pick-up device of the invention, the pick-up body may comprise: information light generation means for generating information light carrying information; recording-specific reference light generation means for generating recording-specific reference light; reproduction-specific reference light generation means for generating reproduction-specific reference light; a recording/reproducing optical system for irradiating the optical information recording medium with the information light and the recording-specific reference light from the same side so that information is recorded on the optical information recording medium in the form of an interference pattern resulting from interference between the information light and the recording-specific reference light, and for irradiating the optical information recording medium with the reproduction-specific reference light and collecting reproduction light generated from the optical information recording medium on the same side as that from which the optical information recording medium is irradiated with the reproduction-specific reference light; and detection means for detecting the reproduction light collected by the recording/reproducing optical system. In this case, the recording/reproducing optical system may perform the irradiation with the information light, the recording-specific reference light and the reproduction-specific reference light and the collection of the reproduction light so that an optical axis of the information light, an optical axis of the recording-specific reference light, an optical axis of the reproduction-specific reference light, and an optical axis of the reproduction light are located on the same line. In addition, the information light generation means may modulate light spatially, and the detection means may detect a spatial modulation pattern of light.
The other objects, features, and advantages of the invention will become fully apparent from the following description.